Evaluating the Adequacy of Critical Habitat

Movement, demographics, and occupancy dynamics of a federally-threatened salamander: evaluating the adequacy of critical habitat Nathan F. Bendik1, Kira D. McEntire1,2 and Blake N. Sissel1,3 1 Watershed Protection Department, City of Austin, Austin, TX, United States of America 2 Current affiliation: Warnell School of Forestry and Natural Resources, University of Georgia, Athens, GA, United States of America 3 Current affiliation: Natural Resources, Travis County, Austin, TX, United States of America ABSTRACT Critical habitat for many species is often limited to occupied localities. For rare and cryptic species, or those lacking sufficient data, occupied habitats may go unrecognized, potentially hindering species recovery. Proposed critical habitat for the aquatic Jollyville Plateau salamander (Eurycea tonkawae) and two sister species were delineated based on the assumption that surface habitat is restricted to springs and excludes intervening stream reaches. To test this assumption, we performed two studies to understand aspects of individual, population, and metapopulation ecology of E. tonkawae. First, we examined movement and population demographics using capture-recapture along a spring-influenced stream reach. We then extended our investigation of stream habitat use with a study of occupancy and habitat dynamics in multiple headwater streams. Indications of extensive stream channel use based on capture-recapture results included frequent movements of >15 m, and high juvenile abundance downstream of the spring. Initial occupancy of E. tonkawae was associated with shallow depths, maidenhair fern presence and low temperature variation (indicative of groundwater influence), although many occupied sites were far from known springs. Additionally, previously dry sites were three times more likely to be colonized than wet sites. Our results indicate extensive Submitted 11 December 2015 Accepted 23 February 2016 use of stream habitats, including intermittent ones, by E. tonkawae. These areas may Published 15 March 2016 be important for maintaining population connectivity or even as primary habitat Corresponding author patches. Restricting critical habitat to occupied sites will result in a mismatch with actual Nathan F. Bendik, habitat use, particularly when assumptions of habitat use are untested, thus limiting the [email protected] potential for recovery. Academic editor Jean Clobert Subjects Additional Information and Conservation Biology, Ecology, Environmental Sciences, Zoology Declarations can be found on Keywords Multi-strata capture-recapture, Caudata, Dynamic occupancy models, Endangered page 20 species, Eurycea tonkawae, Plethodontidae DOI 10.7717/peerj.1817 Copyright INTRODUCTION 2016 Bendik et al. The term critical habitat refers to legally designated areas essential to the persistence and Distributed under recovery of species, and endangered species law in several nations includes provisions Creative Commons CC-BY 4.0 for protection of these areas. Whether critical habitat has been successful as a tool for OPEN ACCESS species recovery has been debated (Rachlinski, 1997; Hoekstra, Fagan & Bradley, 2002; How to cite this article Bendik et al. (2016), Movement, demographics, and occupancy dynamics of a federally-threatened salamander: evaluating the adequacy of critical habitat. PeerJ 4:e1817; DOI 10.7717/peerj.1817 Taylor, Sucking & Rachlinski, 2005; Kerkvliet & Langpap, 2007), and its shortcomings have been attributed to its practice and implementation rather than its intent (Camaclang et al., 2015). In many cases, data limitation appears to be the reason for inadequate delimitations of critical habitat (Camaclang et al., 2015). Accurate delimitation of habitat essential for the conservation of species requires basic information on both habitat associations and habitat availability (Rosenfeld & Hatfield, 2006). Conservation actions may fall short when this information is inaccurate, incomplete or disregarded (Takekawa & Beissinger, 1989; Turner et al., 2004). In practice, critical habitat is often limited only to known localities, excluding unoccupied habitats that may be important for translocations or colonization (Camaclang et al., 2015). For rare, cryptic or otherwise data-deficient species, areas that are essential to species conservation may be underrepresented by designated critical habitats, particularly if it is limited only to areas known to be occupied. Karst fauna exemplify species that are both cryptic (in the evolutionary and ecological sense) and rare, and are often of conservation concern due to their high rates of endemicity and sensitivity to environmental perturbations (Culver et al., 2000). Among the many dozens of endemic karst fauna inhabiting the Edwards Plateau of central Texas (Reddell, 1994) is a unique group of aquatic salamanders (genus Eurycea), several of which have been at the center of highly publicized, political conflicts over development and the Endangered Species Act (Krausse, 1989; Haurwitz, 1993; Haurwitz, 1995; Chippindale & Price, 2005; Wermund, 2012). Many are federally listed with or without designated critical habitat (E. tonkawae, E. nana, E. waterlooensis, E. sosorum, E. rathbuni), are candidates for listing (E. latitans, E. neotenes, E. sp. Pedernales River Springs Salamander, E. sp. Comal Springs Salamander; US Fish and Wildlife Service, 2009; US Fish and Wildlife Service, 2015a) or are listed but awaiting final critical habitat determinations (E. chisholmensis, E. naufragia; US Fish and Wildlife Service, 2012). When critical habitat was recently proposed for three species (E. chisholmensis, E. naufragia, and E. tonkawae) it was limited to springs and excluded intervening areas of stream and other potential surface habitats (subsurface habitat with 300 m buffers were also proposed; US Fish and Wildlife Service, 2012). Although a few collections of epigean (surface-dwelling) populations of Texas Eurycea have been from stream localities (e.g., Bishop & Wright, 1937; Milstead, 1951; Bruce, 1976), the predominant view has generally been that epigean populations are restricted to the vicinity of springs (Sweet, 1982). This view may persist for several of the following reasons: (1) several high profile, single-site endemic Eurycea species do not occur far beyond their large, highly modified spring habitats (e.g., E. sosorum: Chippindale, Price & Hillis, 1993; E. nana: Diaz et al., 2015; E. waterlooensis: Hillis et al., 2001); (2) ease of collection and high abundances around springs make these areas obvious locations for ecological studies (Sweet, 1982; Bowles, Sanders & Hansen, 2006; Pierce et al., 2010; Bendik et al., 2014); or (3) physiological, morphological, or behavioral adaptations indicate the importance of groundwater-associated habitats to their evolutionary history (Stejneger, 1896; Sweet, 1978; Sweet, 1984; Chippindale et al., 2000; Bendik et al., 2013a). This habitat restriction is in contrast to most other Eurycea species that occupy headwater streams (in addition to seeps and springs) as aquatic larvae and paedomorphs (Petranka, 1998; Tumlison & Cline, 1997; Martin et al., 2012; Steffen et al., 2014). These habitats are also present throughout Bendik et al. (2016), PeerJ, DOI 10.7717/peerj.1817 2/26 the Edwards Plateau where springs emerge to feed headwater streams, potentially creating suitable habitat for salamanders within the stream or linking habitat patches (e.g., spring outlets) as a corridor for dispersal. If intervening surface habitat between spring outlets is important, either for dispersal or as primary habitat, limited critical habitat designations and other conservation policy decisions could miss a crucial aspect of Texas Eurycea ecology, increase the risk of extinction for listed species and decrease their probability of recovery. Therefore, a better understanding of stream habitat and the extent to which these salamanders occupy it is necessary. We performed two studies to examine E. tonkawae ecology at the individual, population and metapopulation scale to understand surface habitat use of this threatened, aquatic salamander endemic to the metropolitan area of Austin, Texas. Our first study was motivated by the surface critical habitat initially proposed for this and two similar species, which was based on the maximum distance (50 m) E. naufragia had been recorded to move during a single study near a spring (US Fish and Wildlife Service, 2012). Using data from repeated capture-recapture surveys during a single season, we generated estimates of superpopulation size at various distances upstream and downstream from the spring, quantified the movement of individuals between these areas, and documented the demographic structure of the population to determine whether the proposed critical habitat boundaries adequately reflect habitat used or potentially used by E. tonkawae. For our second study, we extended our inquiry beyond a single population to a broad- scale study of site occupancy dynamics and habitat associations to determine the extent to which E. tonkawae uses headwater stream habitat. We used multi-season occupancy models to examine habitat characteristics associated with E. tonkawae site occupancy (MacKenzie et al., 2006) and simultaneously modeled habitat suitability dynamics in the context of wet or dry site conditions (e.g., Falke et al., 2012), which may differ among urban and rural streams. Urban streams may exhibit altered hydrologic regimes (Walsh et al., 2005), including artificially enhanced recharge from urban

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